The use of dampening systems is well-known to the lithographic press art. The principal objective of a dampening system is to apply a uniform and evenly distributed quantity of dampening fluid to the plate cylinder of a lithographic press in order to ensure a high quality printed image. If too much dampening fluid is applied to the plate cylinder, the ink will become diluted and/or emulsified, causing the printed image to have a blurred or faded appearance. If too little dampening fluid is applied to the plate cylinder, ink will tend to migrate into non-printing areas, thus compromising the printed image. Thus, it is necessary to have a dampening system which provides a uniform film of dampening fluid to the plate cylinder at a desirable rate.
One method for applying dampening fluid to the lithographic plate is described in U.S. Pat. No. 3,168,037 to Dahlgren. The Dahlgren system employs a water pan in which a rubber-coated metering roller is disposed. A chrome-plated transfer roller is disposed parallel to and tangentially communicates with the metering roller. An applicator roller is disposed parallel to and tangentially communicates with the transfer roller such that a thin film of dampening fluid is ultimately transferred from the water pan to the applicator roller. A separate ink train delivers ink to the form roller which, in turn, delivers both ink and dampening fluid to the plate cylinder. Dahlgren controls the volume of dampening fluid delivered by the system by varying the pressure between the metering and transfer rollers and between the transfer and applicator rollers. An independent drive means is provided to rotate the transfer roller and the applicator roller at different speeds to cause slip therebetween. The slippage further regulates the volume of dampening fluid delivered to the lithographic press by the system.
A second method for the application of a dampening fluid to the plate cylinder of a lithographic press is disclosed in U.S. Pat. No. 4,455,983 to Loudon. Loudon employs a dampening form roller and a metering roller. The rollers are positioned in a parallel relation such that they are in tangential contact with one another. A nip is formed immediately above the points of contact between the two rollers. A reservoir of dampening fluid is maintained at the nip such that a film of dampening fluid is allowed to pass between the rollers. The fluid film is directed along the water form roller to the plate cylinder. Loudon also employs a system for returning excess dampening fluid to the reservoir.
Loudon and Dahlgren disclose what are referred to as "continuous" dampeners. Other dampeners which are considered to be "non-continuous" commonly employ a ductor roller to direct dampening fluid across the width of the plate cylinder. Continuous dampening systems are considered to be superior to non-continuous dampeners due to their ability to deliver a continuous, relatively thin film of dampening fluid to the plate cylinder.